System and methods for operating a solenoid valve

ABSTRACT

A drive circuit for controlling a solenoid valve having a solenoid coil and a poppet that translates therein is provided. The drive circuit includes a first node, a second node, a control circuit, and a flyback circuit. The first node is configured to be energized by a power source to a first voltage. The control circuit is coupled to the first and second nodes, and is configured to: (1) selectively couple the first and second nodes in series with the solenoid coil, and periodically energize the solenoid coil using a pulse-width-modulated (PWM) signal having a frequency and a duty cycle configured to regulate a current conducted through the solenoid coil. The flyback circuit is coupled to the solenoid coil and configured to energize the second node to a second voltage with energy stored in the solenoid coil.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 62/540,630, filed on Aug. 3, 2017, the disclosure of which ishereby incorporated by reference in its entirety.

BACKGROUND

The present disclosure relates generally to fluid distribution systemsand, more particularly, to control systems for operating fluiddispensing valves and methods of use.

In agricultural spraying, precise control of fluid flow through a valveis an important factor in delivering a specified amount of agrochemicalto a specified area. Most agrochemicals such as crop protection agentsand many fertilizers are applied as liquid solutions, suspensions, andemulsions that are sprayed onto the target fields. Certainagrochemicals, such as anhydrous ammonia, are dispensed into soilthrough dispensing tubes positioned behind knives or plows that preparethe soil for application.

Typically, the agrochemical liquid is supplied by powered pumps tosimple or complex orifice nozzles that atomize the liquid stream intospray droplets. Nozzles are often selected primarily on the desiredrange of flow rates needed for the job and secondarily on the range ofliquid droplet size spectra and spray distribution patterns theyproduce.

Increasing concerns over inefficient agrochemical use, the cost ofagrochemicals and inadvertent spray drift or pesticide run-off haveresulted in attempts to improve the quality, precision, accuracy andreliability of application of agrochemicals. This has led to increaseduse of electronic control systems and individual control of spraynozzles or nozzle assemblies through use of solenoid valves.Consequently, the power necessary to operate the solenoid valvesincreases as the number of valves and size of the system increase.Moreover, as fluid flow per valve increases, the necessary powerincreases further. At some point, the total power approaches limits ofthe electrical system, its components, and its conductors, e.g., wiring.

Solenoid valves generally include a solenoid coil, or winding, withinwhich a poppet translates to open and close an orifice. Typically, thepoppet is biased by a spring to the closed position. In operation, acurrent is supplied to the coil to generate a magnetic field thatinduces a force on the poppet. The force on the poppet generally resultsin the solenoid valve's opening or holding a position, against forcessupplied by the spring and the pressure of fluid dispensed through thevalve. Closing of the valve is generally achieved by the spring forcesovercoming the force generated by the solenoid coil. Solenoid valves insprayer systems are typically operated to deliver an on/off pattern or apulse width modulation (PWM) pattern of fluid through a given valve andnozzle assembly. Under ideal conditions, a PWM fluid delivery patternwould match a PWM control signal in pulse width and duty cycle, implyingan instantaneous opening and closing of the valve. However, opening orclosing of a solenoid valve is not instantaneous due to inertia, fluiddrag, poppet friction, material properties, and inherent electricalcharacteristics of the solenoid coil. The most profound delay inagricultural spray systems is due to the time-varying currentrelationship for a given voltage applied to an inductive coil, such asthe solenoid coil, i.e., V/L=δi/δt. In other words, time is required toincrease current conducted through the solenoid coil, i.e., coilcurrent, to a level sufficient to generate the force necessary tocontrol movement of the poppet.

In practice, such electrical characteristics skew the operational pulsewidth and duty cycle with which the solenoid valve operates with respectto an electrical pulse width and duty cycle that controls the solenoidvalve. Likewise, the skew applies to the application of fluid itself.

Another component of the time delay in opening the solenoid valves isthe fluid pressure differential across the orifice. Generally, as thedifferential pressure increases, the force necessary to translate thepoppet to the open position increases, thus, according to the electricalcharacteristics described above, increasing the time required to openthe valve. Conversely, the differential pressure is mitigated in certaintypes of valves, such as, for example, pressure-compensated valves. Therelationship between valve opening time and current is typicallynon-linear and similar to that of an inductive coil current over time.The relationship between fluid pressure and open time is increasinglynon-linear as coil current approaches the asymptotic limit for thesolenoid coil. Consequently, an upper limit exists, referred to as themaximum operating pressure differential (MOPD), at which the solenoidvalve cannot be opened due to the maximum current for a given voltageapplied to the inductive coil.

Thus, a need currently exists for a system and process for rapid,precise, and predictable opening and closing of solenoid valves. Such asystem and process is well suited for use in the agricultural field. Itshould be understood, however, that similar needs also exist in otherfields. For example, on irrigation systems, in industrial spray driers,and in spray humidification or cooling systems. Specifically, a systemthat provides rapid and precise opening and closing of solenoid valvesmay find wide applicability in any system, whether commercial,industrial or residential, that utilizes solenoid valves.

BRIEF DESCRIPTION

In one aspect, a drive circuit for controlling a solenoid valve having asolenoid coil and a poppet that translates therein is provided. Thedrive circuit includes a first node, a second node, a control circuit,and a flyback circuit. The first node is configured to be energized by apower source to a first voltage. The control circuit is coupled to thefirst and second nodes, and is configured to: (1) selectively couple thefirst and second nodes in series with the solenoid coil, andperiodically energize the solenoid coil using a pulse-width-modulated(PWM) signal having a frequency and a duty cycle configured to regulatea current conducted through the solenoid coil. The flyback circuit iscoupled to the solenoid coil and configured to energize the second nodeto a second voltage with energy stored in the solenoid coil.

In another aspect, a method of controlling a solenoid valve having asolenoid coil and a poppet configured to translate therein is provided.The method includes (1) energizing a first node to a first voltage usinga power source, (2) coupling the first node to the solenoid coil andenergizing the solenoid coil using a pulse-width-modulated (PWM) signalhaving a frequency and a duty cycle configured to regulate a currentconducted through the solenoid coil to below an opening threshold tomaintain the poppet in a closed position, (3) energizing a second nodeto a second voltage with energy stored in the solenoid coil using aflyback circuit coupled to the solenoid coil, (4) coupling the secondnode to the solenoid coil and energizing the solenoid coil using a DCsignal configured to increase the current to above the opening thresholdto translate the poppet toward an opened position, and (5) coupling thefirst node to the solenoid coil and energizing the solenoid coil usingthe PWM signal having a frequency and a duty cycle configured toregulate the current to above a closing threshold to maintain the poppetin the opened position.

These and other features, aspects and advantages of the presentdisclosure will become better understood with reference to the followingdescription and appended claims. The accompanying drawings, which areincorporated in and constitute a part of this specification, illustrateembodiments of the disclosure and, together with the description, serveto explain the principles of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of one embodiment of an agricultural spraysystem;

FIG. 2 is a perspective view of one embodiment of a nozzle assemblysuitable for use with the agricultural spray system of FIG. 1;

FIG. 3A and FIG. 3B are sectional views of a portion of a solenoid valvesuitable for use in the nozzle assembly shown in FIG. 2;

FIG. 4 is a schematic diagram of a drive circuit for use with thesolenoid valve shown in FIG. 3;

FIG. 5 is a flow diagram of an exemplary method of controlling thesolenoid valve shown in FIG. 3;

FIG. 6 is a plot of exemplary signals present in the drive circuit shownin FIG. 4;

FIG. 7 is a schematic diagram of an exemplary drive circuit for use withthe solenoid valve shown in FIG. 3;

FIG. 8 is a plot of exemplary signals present in the drive circuit shownin FIG. 7;

FIG. 9 is a schematic diagram of another exemplary drive circuit for usewith the solenoid valve shown in FIG. 3;

FIG. 10 is a perspective view of a fluid application system; and

FIG. 11 is a perspective view of a portion of the fluid applicationsystem shown in FIG. 7.

Corresponding reference characters indicate corresponding partsthroughout the several views of the drawings.

DETAILED DESCRIPTION

It is realized herein that by increasing the operating voltage of thesolenoid valve, the time delays resulting from electricalcharacteristics and fluid pressure in opening the solenoid valve arereduced. For example, in agricultural spray systems, the operatingvoltage of solenoid valves may be increased from 12 Volt (V) directcurrent (DC) to 24 Volt DC or more. It is further realized herein that24 Volt DC is typically unavailable on agricultural equipment. Moreover,increasing to 24 Volt DC would increase power dissipation by thesolenoid coil, and would potentially exceed electrical ratings for thesolenoid coil itself, wiring, or other electrical components on a givenagricultural spray system.

It is realized herein the required force is at its peak when translatingthe poppet from the closed position to the open position, which is whenthe combined countervailing forces of the fluid pressure and a springpre-loading of the poppet are at their peak. More specifically, springforces on the poppet increase as the spring is compressed withtranslation toward the opened position, but fluid pressure across thevalve drops significantly when the poppet translates from the closedposition. Conversely, the required force for holding the poppet in anopened position is significantly reduced from that necessary to open thesolenoid valve. Accordingly, it is realized herein, the operatingvoltage of the solenoid valve may be increased momentarily when openingthe solenoid valve to reduce the turn-on time delay, thereby reducingthe time necessary to reach a coil current sufficient to translate thepoppet to the open position. Further, the coil current may be reducedwhen holding the poppet in the opened or closed state to conserve power.

It is realized herein, given that agricultural equipment typically lack,for example, a 24 Volt DC power source, an additional power source isneeded for generating the increased potential across the solenoid valve.Such a power source, in certain circumstances, may be an additionalbattery or power supply. In many agricultural spray systems, it may bepreferred to provide a converter circuit for generating, for example,the 24 Volt DC power from a 12 Volt DC source. However, the cost andadded complexity, size, and weight of converter circuits, including, forexample, a switching boost converter, may be prohibitive.

A typical switching boost converter includes an inductive coil that,when energized with a PWM current signal at a first voltage (e.g., a lowvoltage), stores an electromagnetic field that, when current amplitudeis reduced, generates a flyback voltage across the inductive coil thatis captured and used to energize a bus, or “node,” to a second voltagethat is either higher than the first voltage or that is a negativevoltage. It is realized herein a switching boost converter circuit maybe constructed utilizing a solenoid coil of a solenoid valve as thenecessary inductive coil. Further, in certain embodiments, a drivecircuit for controlling such a solenoid valve may include various othercomponents, in addition to the inductive coil, necessary forconstructing the switching boost converter. It is further realizedherein the inductive coil of the switching boost converter is typicallythe most expensive, largest, and heaviest component in the device. Aspower requirements increase, the size and cost of the inductive coilstend to increase as well.

It is realized herein current supplied to the solenoid coil of asolenoid valve in a spray system can be regulated to both provide a PWMfluid pattern based on periodic opening and closing of the solenoidvalve, and operate as a switching boost converter to energize a secondnode that is a high voltage bus or, in the alternative, a negativevoltage bus, or “sub-ground.” It is further realized herein the secondnode may be used to energize the solenoid coil during opening to improvethe speed, precision, and predictability of valve opening, and alsoimproving MOPD.

One exemplary agricultural spray system may operate valves at about 10Hertz, i.e., a given solenoid valve is opened every 100 milliseconds(ms) according to a valve-pulsing PWM signal. The solenoid valve maytake about 6 ms to open and about 4 ms to close. For the remainder ofthe 100 ms period, the solenoid valve maintains the poppet in the openedor closed position, otherwise referred to as idle time. Typically, whena solenoid valve is activated, i.e., opened and held open, the solenoidcoil is energized continuously and, conversely, when the solenoid valveis deactivated, i.e., closed and held close, the solenoid coil isde-energized. It is realized herein the frequency and duty cycle of thecurrent conducted through the solenoid coil may be regulated tocontinuously conduct current through the solenoid coil while maintainingthe control of the desired valve-pulsing PWM signal.

The frequency and duty cycle may be regulated for four distinctdurations: (1) holding the poppet in a closed position, (2) translatingthe poppet from the closed position to the opened position, (3) holdingthe poppet in the opened position, and (4) translating the poppet fromthe opened position to the closed position.

When holding the poppet in the closed position, a first voltage (e.g., alow voltage such as 12 VDC) is applied to the solenoid coil and the coilis energized using a PWM signal such that the current conducted throughthe solenoid coil is regulated to below the opening threshold, i.e., thethreshold current for opening the solenoid valve. Rather than keepingthe solenoid coil de-energized, as is typical, maintaining some currentthrough the solenoid coil enables energy to be continuously stored inthe solenoid coil. During the PWM period and during any of the abovedurations, when the solenoid coil is de-energized, energy stored in thesolenoid coil is recovered by a flyback circuit that charges a secondnode, i.e., the solenoid coil and flyback circuit form a switched boostconverter.

The PWM signal is regulated in frequency and duty cycle to both maintaincurrent conducted through the solenoid coil below the opening thresholdand to optimize performance of the flyback circuit for charging thesecond node. When the first voltage is applied to the solenoid coil,e.g., when holding the poppet in the closed position and charging thesecond node, the rate at which the second node is charged is directlyrelated to the power stored in the solenoid coil, which is based on thecurrent conducted through the solenoid coil and the inductance of thecoil. This is also related to the voltage applied to the solenoid coiland the inductance of the solenoid coil, i.e., the first voltage and theinductance defined by the solenoid coil. The inductive current curve isgenerally non-linear near the asymptotic current limit, and becomes morelinear as current moves toward zero. However, the rate at which thesolenoid coil discharges through the flyback circuit and onto the secondnode increases as the charge on the second node increases. Accordingly,it is realized herein, frequency and duty cycle of the PWM signal may beadjusted continuously to maintain a target coil current as the secondnode charges. Generally, for a given frequency, as the duty cycle of thePWM signal increases, more of the cycle time is spent storing energy inthe solenoid coil and less of the cycle time is spent discharging thesolenoid coil through the flyback circuit to charge the second node.Conversely, decreasing the duty cycle allots more time for discharge andless time for charging. Further, increasing the frequency of the PWMsignal shortens the period of the PWM cycle and, consequently, reducesthe time available for both charging and discharging the solenoid coil.Generally, a higher frequency PWM signal yields lower peak-to-peakcurrent levels through the solenoid coil, and a lower frequency PWMsignal lengthens cycle times and allots more time for charging anddischarging the solenoid coil.

Referring again to holding the poppet in the closed position, the PWMsignal is regulated, for example, to a low frequency and a low dutycycle to hold the coil current just below the opening threshold, whilemaximizing discharge (of the solenoid coil) time to charge the secondnode through the flyback circuit. The duty cycle of the PWM signal maybe, for example, in the range of 10% to 50%. The valve is operated,i.e., opened and closed, in a frequency range of about 3-40 Hertz. Thelow frequency PWM signal may have a frequency in a range of, forexample, 100 Hertz to 5 kilohertz. The frequency and duty cycle for agiven solenoid valve may vary from these ranges according to the size,i.e., inductance of the solenoid coil, as well as the various parametersthat define the opening threshold. In certain embodiments, frequency ofthe PWM signal may be increased just before opening, e.g., about 5 msbefore opening, to ramp up coil current leading up to opening thesolenoid valve. In such embodiments, the frequency of the PWM signal maybe increased to above 1000 Hertz. In certain embodiments, the frequencymay be increased to a range of 4 kilohertz to 100 kilohertz depending onthe size of the solenoid valve.

When the solenoid valve is to be opened, i.e., the poppet translatesfrom the closed position to the opened position, a second voltage,sourced from the second node, is applied to the solenoid coil inaddition to the first voltage from a first node, or power source, andthe coil is energized using 100% duty cycle DC signal to increase thecoil current above the opening threshold as quickly as possible. Incertain embodiments, the second node is charged to a high voltage thatis larger than the first voltage (e.g., 24 VDC versus 12 VDC on thefirst node). In alternative embodiments, the second node is charged to alarge negative voltage (e.g., −24 VDC). The large potential resultingfrom the series-combined voltage sources (i.e., first and second nodes,or e.g., low voltage bus and high voltage bus) and high (i.e., 100%)duty cycle PWM signal combine to provide a fast opening time. Moreover,the coil current leading up to the opening is preferably maintained justbelow the opening threshold, thereby minimizing the time required toincrease the current through the solenoid coil to above the openingthreshold. Accordingly, the delay in opening the solenoid valve isreduced.

When the solenoid valve is opened, there is a duration when the poppetis maintained in the opened position. Generally, the power necessary tohold the poppet in an opened position is much less than the powernecessary to translate the poppet to the opened position. It is realizedherein that once the poppet is in the opened position, the potential onthe second node may be removed from the solenoid coil, i.e., leaving thefirst voltage of the first node (e.g., lower voltage), and duty cyclemay be reduced, i.e., a PWM signal, to reduce the power consumption ofthe solenoid valve. The coil current is regulated to just above aclosing threshold, i.e., a current threshold below which the forcegenerated by the solenoid coil is insufficient to hold the poppet in theopened position. Likewise, when the solenoid coil is de-energized duringthe PWM period, energy stored in the solenoid coil is recovered by theflyback circuit that charges the second node.

When holding the poppet in the opened position, coil current isregulated to above the closing threshold. Accordingly, the frequency andduty cycle of the PWM signal are regulated to hold the coil current justabove the closing threshold and to optimize performance of the flybackcircuit in charging the second node. Moreover, the frequency and dutycycle are regulated to reduce power consumption when the poppet is notbeing translated. Duty cycle is regulated to maintain coil current justabove the closing threshold and to allot as much time as possible todischarge the solenoid coil through the flyback circuit to charge thesecond node. In certain embodiments, for example, duty cycle isregulated to a range of 40% to 90%. As described above, this range ofduty-cycle may vary for a given solenoid valve. Frequency of the PWMsignal, in certain embodiments, is held high, for example, in a range of1000 to 2000 Hertz, to provide lower peak-to-peak coil current levelsand, consequently, tighter control to hold coil current just above theclosing threshold. In certain embodiments, the frequency may droop tolengthen the cycle and the duty cycle reduced to allot additionaldischarge time for the solenoid coil. In certain embodiments, frequencyand duty cycle may only be increased a short duration, e.g., 5milliseconds, before the solenoid valve is to be closed. In suchembodiments, the frequency and duty cycle of the PWM signal may beoptimized to charge the second node until the short duration beforeclosing the solenoid valve. In certain embodiments, the currentconducted through the solenoid coil is monitored and the measurementused to dynamically control the frequency and duty cycle of the PWMsignal to charge the second node.

When the solenoid valve is to be closed, voltage is removed from thesolenoid coil to reduce the coil current to below the closing threshold.In certain embodiments including a charge pump circuit, the charge pumpcircuit would also be allowed to float (i.e., as an open circuit),allowing the coil current to discharge rapidly (e.g., through a TVSdiode), or configured to speed up dissipation of the solenoid coil(e.g., by re-referencing the charge pump circuit) while charging thecharge pump capacitor. Once the poppet is in the closed position, it isrealized herein, the solenoid coil should continue to conduct a currentto maintain the energy stored in the solenoid coil and to remain readyfor the next opening cycle. Accordingly, the current conducted throughthe solenoid coil is regulated to just below the opening threshold. Incontrast, the solenoid coil is typically de-energized entirely.

In alternative embodiments, the advantages described above for the useof a second voltage (e.g., a higher voltage or a negative voltage) whenopening the solenoid valve can be achieved using solenoid coils havingsimilar magnetic characteristics and a lower internal resistance, andthus, a lower constant voltage rating due to power dissipation. Such aconfiguration enables faster turn-on times without providing a separatehigh voltage bus supplied by a separate power supply. The openingoperation of the solenoid valve is generally unchanged, however, onceopened, the voltage applied across the solenoid coil can be reduced,i.e., divided, by coupling multiple solenoid coils for multiple solenoidvalves in series, i.e., daisy-chaining solenoid coils. Moreover, inother embodiments, coil current may be throttled as described herein toreduce overall power consumption.

In further alternative embodiments, the solenoid valve and solenoid coilmay be designed to fit the drive circuit and the achievable voltagelevels. Such optimization ensures power ratings of the solenoid coil areacceptable for the power levels applied to the solenoid valve.

Referring now to the Figures, FIG. 1 is a perspective view of oneembodiment of a spray system, indicated generally at 10, operativelyconnected to a work vehicle 12. As shown, work vehicle 12 includes a cab14 and a plurality of wheels 16. Work vehicle 12 may in certainembodiments be an agricultural tractor having any suitableconfiguration. However, it should be appreciated that in otherembodiments, any other suitable aero or ground means may be provided formoving spray system 10. For example, in other embodiments, work vehicle12 may not include a cab, and instead may have any suitable operatorstation. Further, in some embodiments, work vehicle 12 and/or spraysystem 10 may include a global positioning system (e.g., a GPS receiver)for automated control of work vehicle 12 and/or spray system 10. In someembodiments, the global positioning system is used to monitor a travelspeed of vehicle 12 and/or spray system 10, and/or to monitor a positionof work vehicle 12 and/or spray system 10.

In the example embodiment, spray system 10 includes at least one boomwheel 18 for engaging a section of ground with a crop, produce, productor the like (generally, P), a tank or reservoir 22, and a spray boom 24.Spray boom 24 includes a plurality of nozzle assemblies 34 attachedthereto and in fluid communication with tank 22. Tank 22 holds a productS, such as a liquid, a mixture of liquid and powder, or other product.Product S may be a quantity of water or an agrochemical such as afertilizer or a pesticide, and may be sprayed from nozzle assemblies 34onto, for example, a crop or produce or ground P itself, as shown inFIG. 1 and described in greater detail below. It should be appreciated,however, that in other embodiments, system 10 may have any othersuitable configuration. For example, in other embodiments, system 10 maynot include boom wheel 18 or may alternatively include any suitablenumber of boom wheels 18. Further, while work vehicle 12 is depicted astowing spray system 10 in the example embodiment, it should beappreciated that, in other embodiments, work vehicle 12 may transportspray system 10 in any suitable manner that enables spray system 10 tofunction as described herein.

The quantity of product S held in tank 22 generally flows through aconduit to nozzle assemblies 34. More specifically, in the embodimentillustrated in FIG. 1, product S flows from tank 22, through a pipe 30to a boom pipe 32, and from boom pipe 32 to nozzle assemblies 34. Incertain embodiments, nozzle assemblies 34 comprise direct actingsolenoid valve equipped nozzles (see, e.g., FIG. 2) and system 10 mayinclude a pump, transducers to measure fluid pressure and fluid flow,sectional regulating valves, and a pressure and/or flow controller (notshown in FIG. 1). If included, the pump may be positioned downstreamfrom tank 22, upstream from boom pipe 32 and nozzle assemblies 34, andin operative communication with a controller for controlling operationthereof. The pump may be a pulse width modulation controlled pumpconfigured to provide a desired amount of product S flow through system10. The spray system 10 may also include a pressure or flow controllerconfigured to vary certain operating parameters of the pump, such as thepump's pulse frequency and/or duty cycle, to obtain a desired productflow rate through system 10.

Referring still to FIG. 1, product S flows through nozzle assemblies 34and may be applied to ground P in various ways. For example, product Smay flow from nozzle assemblies 34 in a pulsed pattern. It should beappreciated that terms “pipe” and “conduit,” as used herein, may meanany type of conduit or tube made of any suitable material such as metalor plastic, and moreover that any other suitable ground applicationdevices can be added to provide varying effects of placement of productS on top or below a soil surface of ground P, such as via pipes, knives,coulters, and the like.

FIG. 2 is a perspective view of one embodiment of a nozzle assembly 34suitable for use with spray system 10 of FIG. 1. As shown in FIG. 2,nozzle assembly 34 generally includes a valve assembly 36, a nozzle body37 configured to receive product S flowing through boom pipe 32 and aspray nozzle 39 mounted to and/or formed integrally with nozzle body 37for expelling product S from nozzle assembly 34 onto crops, productand/or ground P.

In some embodiments, valve assembly 36 is a solenoid valve (see, e.g.,FIG. 3). Moreover, in some embodiments, valve assembly 36 may beconfigured to be mounted to and/or integrated with a portion of spraynozzle 39. In some embodiments, for example, valve assembly 36 may bemounted to the exterior of nozzle body 37, such as by being secured tonozzle body 37 through the nozzle's check valve port. Alternatively,valve assembly 36 may be integrated within a portion of nozzle body 37.

FIGS. 3A and 3B are schematic cross-sectional views of one embodiment ofan electric solenoid valve 300 suitable for use in nozzle assembly 34shown in FIG. 2. FIG. 3A illustrates solenoid valve 300 in a closedposition. FIG. 3B illustrates solenoid valve 300 in an open position. Ingeneral, valve 300 includes an inlet 302 and an outlet 304 for receivingand expelling fluid 306 from valve 300. Valve 300 also includes asolenoid coil 308 located on and/or around a guide 310. For instance, inone embodiment, solenoid coil 308 is wrapped around guide 310.Additionally, an actuator or poppet 312 is movably disposed within guide310. In particular, poppet 312 may be configured to be linearlydisplaced within guide 310. Moreover, as shown, valve 300 includes aspring 314 coupled between guide 310 and poppet 312 for applying a forceagainst poppet 312 to bias poppet 312 towards the closed position. Valve300 may also include a valve body 316 or other outer covering disposedaround coil 308.

As shown in the illustrated embodiment, valve 300 is configured as anin-line valve. Thus, fluid 306 may enter and exit valve 300 throughinlet 302 and outlet 304, respectively, along a common axis 318. Inother words, the inlet 302 and outlet 304 may generally be aligned alongaxis 318. In alternative embodiments, valve 300 may be in any othersuitable configuration for a solenoid valve, such as, for example, acounter flow valve or a pressure-compensated valve.

In addition, solenoid coil 308 may be coupled to a controller (notshown) configured to regulate or control the current provided to coil308. The controller may be enclosed within valve assembly 300, may beenclosed within nozzle assembly 34, as shown in FIG. 2, or may existsome distance away from nozzle assembly 34. The controller may generallycomprise any suitable computer and/or other processing unit, includingany suitable combination of computers, processing units and/or the likethat may be communicatively coupled to one another (e.g., a controllermay form all or part of a controller network). Thus, the controller mayinclude one or more processor(s) and associated memory device(s)configured to perform a variety of computer-implemented functions (e.g.,performing the methods, steps, calculations and/or the like disclosedherein). As used herein, the term “processor” refers not only tointegrated circuits referred to in the art as being included in acomputer, but also refers to a controller, a microcontroller, amicrocomputer, a programmable logic controller (PLC), an applicationspecific integrated circuit, and other programmable circuits.Additionally, the memory device(s) of the controller may generallycomprise memory element(s) including, but not limited to, computerreadable medium (e.g., random access memory (RAM)), computer readablenon-volatile medium (e.g., a flash memory), a floppy disk, a compactdisc-read only memory (CD-ROM), a magneto-optical disk (MOD), a digitalversatile disc (DVD) and/or other suitable memory elements. Such memorydevice(s) may generally be configured to store suitablecomputer-readable instructions that, when implemented by theprocessor(s), configure the controller to perform various functionsincluding, but not limited to, controlling the current supplied tosolenoid coil 308, monitoring inlet and/or outlet pressures of thedisclosed valve(s), monitoring poppet operation of the disclosed valves,receiving operator inputs, performing the calculations, algorithmsand/or methods described herein and various other suitablecomputer-implemented functions.

Coil 308 may be configured to receive a controlled electric current orelectric signal from the controller such that poppet 312 may move withinguide 310. For example, in one embodiment, the controller includes adrive circuit as shown in FIG. 4, or any other suitable device that isconfigured to apply a regulated current to coil 308, thereby creating amagnetic field that biases (by attraction or repulsion) poppet 312towards the opened or closed position. As a result, poppet 312 may bemoved to a proper throttling position for controlling the pressure dropacross valve 300. Additionally, the attraction between coil 308 andpoppet 312 may also allow poppet 312 to be pulsated or continuouslycyclically repositioned, thereby providing for control of the averageflow rate through valve 300.

In several embodiments, a modulated square wave (e.g., PWM signal)drives valve 300 to control the opening and closing. A “pulse”corresponds to a duration (e.g., a 100 millisecond cycle) in which a lowfrequency duty cycle value (e.g., at a frequency of less than 40 Hz)sets the amount of on/off time. The “off” time may correspond to a “coildischarging period” in which the drive voltage is turned offcontinuously and a “modulated period” in which the voltage is turned onand off at a high frequency (e.g., at a frequency of greater than 100Hz). The PWM signal is used to hold poppet 312 in the open or closedposition. The frequency and duty cycle of the PWM signal are used toregulate coil current and at least partially open valve 300 by movingpoppet 312 to the open position. The duration of the coil discharging(or charging) period may be determined by the amount of time for thecoil current to reach the desired value. The coil current may becontinuously measured and compared to a threshold in order to controlpower to coil 308.

Forces from spring 314, fluid 306 and coil 308 act on poppet 312simultaneously. Specifically, the forces from spring 314 and fluid 306,tend to bias poppet 312 towards the closed position, while the forcefrom coil 308 tends to bias poppet 312 towards the opened position.

Thus, when valve 300 is unpowered (i.e., when a voltage is not appliedacross coil 308), spring 314 and the pressure differential across thevalve 300 may force poppet 312 towards the closed position such that thesystem pressure has a tendency to force valve 300 into a sealed orclosed position. In such an embodiment, poppet 312 may include a rubberdisk or any other suitable sealing member 320 configured to pressagainst an orifice 322 of outlet 304 to create a leak-free seal on valve300 when valve 300 is in the closed position. Additionally, when valve300 is powered (i.e., when a voltage is applied to coil 308), poppet 312may be attracted by coil 308 away from orifice 322 such that poppet 312is moved to the open position. Specifically, the current supplied tocoil 308 may be controlled such that the force acting on poppet 312 bycoil 308 is sufficient to position poppet 312 a predetermined distancefrom orifice 322 of valve 300, thereby opening valve 300.

When valve 300 is being pulsed, the movement of poppet 312 may be cycledbetween the open position and a closed position, wherein poppet 312 issealed against orifice 322. In such an embodiment, in order totransition valve 300 from the closed position to the open position,valve 300 is initially energized with a 100% duty cycle to move poppet312 from the closed position to the open position as quickly aspossible. Subsequently, the current supplied to coil 308 may becontrolled such that poppet 312 may be cyclically pulsed between theclosed position and the open position.

The sizes of inlet 302 and outlet 304, as well as the geometry and/orconfiguration of poppet 312 and guide 310, may be chosen such that theforce acting on poppet 312 from coil 308 may overcome the fluid forcesand spring forces for every throttling position within the total strokeof valve 300 when the coil is fully powered. Similarly, in oneembodiment, spring 314 may be sized such that the spring forcecorresponds to the minimal amount of force required to maintain adrip-free valve 300 when valve 300 is unpowered. Additionally, in someembodiments, variable rate springs and/or partial springs may beselected to tune a particular valve design.

Generally, the solenoid valve 300 may be utilized to control the flowthrough any suitable device. However, in several embodiments of thepresent disclosure, the solenoid valve 300 may be used to control theflow through an agricultural spray nozzle. In such embodiments, thedisclosed solenoid valve 300 may be configured as part of a nozzleassembly for use with various agricultural spraying systems.

Although systems and methods are described herein with reference to anagricultural spray system, embodiments of the present disclosure aresuitable for use with agricultural fluid application systems other thanspray systems. In some embodiments, for example, the systems and methodsof the present disclosure are implemented in a fluid application systemthat injects fluid, such as fertilizer, into the soil through dispensingtubes, rather than spray nozzles.

FIG. 4 is a schematic diagram of a drive circuit 400 for use with thesolenoid valve shown in FIG. 3. Drive circuit 400 includes a low voltagebus 402 (a first node) and a high voltage bus 404 (a second node). Lowvoltage bus 402 is configured to be energized by a power source, suchas, for example, a 12 Volt DC power supply. High voltage bus 404 isconfigured to be energized by a flyback circuit 406 coupled to solenoidcoil 308. In one embodiment, low voltage bus 402 is charged to 12 VoltDC and high voltage bus 404 is charged to 24 Volt DC. In alternativeembodiments, voltages of low voltage bus 402 and high voltage bus 404may vary over time. For example, low voltage bus 402 is ideally chargedto 12 Volt DC, but varies over time from 11-14 Volt DC. Likewise, thevoltage to which high voltage bus 404 is charged may vary over time andmay exceed 24 Volt DC. For example, in one embodiment, high voltage bus404 is charged up to 36 Volts DC.

Drive circuit 400 includes a switch 408 for selectively coupling highvoltage bus 404 to solenoid coil 308. For example, switch 408 isillustrated as a PFET device controlled by a switching signal 410 tocouple and decouple high voltage bus 404 to solenoid coil 308. Drivecircuit 400 is configured to be coupled to a controller (not shown) thatgenerates switching signal 410 according to a valve-pulsing PWM signalthat initiates opening of the solenoid valve, such as solenoid valve 300shown in FIG. 3.

Drive circuit 400 includes a switch 412 that periodically couplessolenoid coil 308 to ground, thereby enabling solenoid coil 308 toconduct current. For example, switch 412 is illustrated as a NFET devicecontrolled by a switching signal 414 generated by a controller (notshown). Switch 412 applies a PWM signal to solenoid coil 308 to energizesolenoid coil 308 while holding poppet 312 in position, e.g., in theopened or closed positions. Switch 412 is operated at a frequency andduty cycle, thereby regulating the frequency and duty cycle of the PWMsignal that energizes solenoid coil 308. Switch 412 is opened and closedwhen closing and opening valve 300, respectively. Switch 412 is closedto apply a 100% duty cycle DC voltage to solenoid coil 308 when openingvalve 300. Likewise, switch 412 is opened to remove power from solenoidcoil 308 when closing valve 300.

Switches 408 and 412 at least partially compose a control circuit 416.In certain embodiments, control circuit 416 includes a current sensor,such as current sense resistor 418 configured to measure the currentconducted through solenoid coil 308. Control circuit 416 may thenregulate the frequency and duty cycle of the current conducted throughsolenoid coil 308 by controlling switch 412 based on the coil currentmeasured by current sense resistor 418. In alternative embodiments,control circuit 416 includes any other suitable device for measuringcurrent through solenoid coil 308, such as, for example, a hall-effectsensor. In further alternative embodiments, control circuit 416 isconfigured to measure current through solenoid coil 308 when solenoidcoil 308 is charging, and further configured to predict discharge timeof solenoid coil 308 based on the potential on high voltage bus 404. Incertain embodiments, a current sense resistor may be used to determinethe discharge time of solenoid coil 308 based on a measured currentconducted through solenoid coil 308. The determined discharge time ormeasured current may then be further utilized in determining a desiredfrequency and duty cycle of the PWM signal.

Flyback circuit 406 includes a feed diode 420, an over-voltageprotection diode 422, and a capacitor 424. When switch 412 periodicallyde-energizes solenoid coil 308 according to the PWM signal, energystored in solenoid coil 308 builds an opposite-polarity voltage acrosssolenoid coil 308 that is steered by feed diode 420 to build a chargeacross capacitor 424. The resulting voltage across capacitor 424represents high voltage bus 404.

The frequency and duty cycle of the PWM signal generated by switch 412is regulated for four distinct durations: (1) holding poppet 312 in aclosed position, (2) translating poppet 312 from the closed position tothe opened position, (3) holding poppet 312 in the opened position, and(4) translating poppet 312 from the opened position to the closedposition.

When holding poppet 312 in the closed position, a low voltage, suppliedby low voltage bus 402, is applied to solenoid coil 308 and solenoidcoil 308 is energized by a PWM signal, via switch 412, such that thecurrent conducted through solenoid coil 308 is regulated to below theopening threshold, i.e., the threshold current for opening solenoidvalve 300. Maintaining some current through solenoid coil 308 enablesenergy to be continuously stored in solenoid coil 308, i.e., solenoidcoil 308 is charged. During the PWM period, when solenoid coil 308 isde-energizing, energy stored in solenoid coil 308 is discharged andrecovered by flyback circuit 406 that charges high voltage bus 404,i.e., solenoid coil 308 and flyback circuit 406 form a switched boostconverter. Switch 412 is configured to regulate duty cycle and frequencyof the PWM signal to hold the coil current below the opening thresholdand to charge high voltage bus 404.

When solenoid valve 300 is to be opened, i.e., poppet 312 translatesfrom the closed position to the opened position, a high voltage, sourcedfrom high voltage bus 404, is applied, via switch 408, to solenoid coil308 and solenoid coil 308 is energized using a 100% duty cycle DCsignal, via switch 412, to drive the coil current above the openingthreshold as quickly as possible. Moreover, the coil current leading upto the opening is preferably maintained just below the openingthreshold, thereby minimizing the time required to increase the coilcurrent above the opening threshold. Accordingly, the delay in openingsolenoid valve 300 is reduced.

In an alternative embodiment, when solenoid valve 300 is to be opened,the low voltage, sourced from low voltage bus 402, is initially appliedto solenoid coil 308 for a duration of, for example, 8 ms, after whichthe high voltage, sourced by high voltage bus 404, is applied tosolenoid coil 308. The additional voltage applied to solenoid coil 308pushes the coil current above the opening threshold and can increase theMOPD of the solenoid valve and reduce the turn-on time.

When solenoid valve 300 is opened, there is a duration when poppet 312is maintained in the opened position. Generally, the power necessary tohold poppet 312 in an opened position is much less than the powernecessary to translate poppet 312 to the opened position. It is realizedherein that once poppet 312 is in the opened position, the high voltagemay be replaced by the low voltage that is applied by a PWM signal, viaswitch 412, to reduce the power consumption of solenoid valve 300. Thecoil current is regulated to just above a closing threshold, i.e., acurrent threshold below which the force generated by solenoid coil 308is insufficient to hold poppet 312 in the opened position. When solenoidcoil 308 is de-energized during the PWM period, energy stored insolenoid coil 308 is recovered by flyback circuit 406 that charges highvoltage bus 404.

When solenoid valve 300 is to be closed, switch 412 opens and solenoidcoil 308 is de-energized to reduce the coil current to below the closingthreshold as quickly as possible. In at least some embodiments, theclosing threshold is nearly zero amperes. In alternative embodiments,the closing threshold may be greater than zero amperes. In suchembodiments, the current conducted through solenoid coil 308 is reducedto below the closing threshold, e.g., zero, for at least a sufficientduration to close solenoid valve 300. In certain embodiments, oncesolenoid valve 300 is closed, solenoid coil 308 continues to conduct acurrent to maintain the energy stored in solenoid coil 308 and to remainready for the next opening cycle. Accordingly, in such embodiments, thecurrent conducted through solenoid coil 308 is regulated to just belowthe opening threshold.

FIG. 5 is a flow diagram of a method 500 of controlling solenoid valve300 (shown in FIG. 3) using, for example, drive circuit 400 (shown inFIG. 4). Method 500 includes energizing 510 low voltage bus 402 using apower source. Method 500 includes coupling 520 low voltage bus 402 tosolenoid coil 308 and energizing solenoid coil 308 using a PWM signalhaving a frequency and duty cycle configured to regulate a currentconducted through solenoid coil 308 to below an opening threshold tomaintain poppet 312 in a closed position.

Method 500 includes energizing 530 high voltage bus 404 with energystored in solenoid coil 308 using flyback circuit 406 coupled tosolenoid coil 308.

Method 500 includes coupling 540 high voltage bus 404 to solenoid coil308 and energizing solenoid coil 308 using a DC signal configured toregulate the current to above the opening threshold to translate poppet312 toward an opened position.

Method 500 includes coupling 550 low voltage bus 402 to solenoid coil308 and energizing solenoid coil 308 using the PWM signal having a dutycycle and frequency configured to regulate the current to above aclosing threshold to maintain poppet 312 in the opened position.

FIG. 6 is a plot 600 of exemplary signals present in drive circuit 400,shown in FIG. 4. Plot 600 illustrates signals over a horizontal timeaxis 602 expressed in ms and ranging from zero to about 250 ms. Plot 600illustrates signals on a vertical axis 604 that represents voltageexpressed in Volts DC and ranging from zero to about 24 Volt DC, orexpressed in Amperes ranging from zero to about 0.6 Amperes. Plot 600includes a PWM signal 606 for controlling switch 412, such as, forexample, switching signal 414 (shown in FIG. 4). Notably, PWM signal 606has a varying frequency and duty cycle. Plot 600 includes a bus voltagesignal 608 representing the high voltage present on high voltage bus 404(shown in FIG. 4). Notably, bus voltage signal 608 increases over timeas it is charged by flyback circuit 406 and is discharged rapidly whensolenoid valve 300 is opened. Plot 600 includes a coil current signal610 representing the buildup of current conducted through solenoid coil308 over time. Notably, coil current signal 610 is generally non-zeroand is highest when opening solenoid valve 300. Further, in certainembodiments, coil current signal 610 may be approximately zero (orotherwise below the closing threshold) for a duration when solenoidvalve 300 is closing.

FIG. 7 is a schematic diagram of an exemplary drive circuit 700 for usewith solenoid valve 300 and solenoid coil 308 shown in FIG. 3. FIG. 8 isa plot 800 of exemplary signals over time, t, present in drive circuit700 shown in FIG. 7. FIG. 8 includes plots of signals 802, 804, 806,808, 810, and 812 with respect to time, t, represented by a horizontaltime axis 814.

Drive circuit 700 includes a low voltage bus 702 and a high voltage bus704. A potential 804 of high voltage bus 704 is illustrated in FIG. 8.Potential 804 is illustrated with respect to a vertical axis for voltageranging from zero Volts DC to 36 Volts DC.

Power supplied to solenoid coil 308 is regulated by a switch 706 and aswitch 708. Switch 706 is illustrated as a PFET device that selectivelycouples high voltage bus 704 to solenoid coil 308. Switch 706 iscontrolled by a PFET control signal 810, illustrated in FIG. 8. PFETcontrol signal 810 is illustrated as a discrete signal, i.e., having anon state and an off state. Switch 708 is illustrated as an NFET devicethat selectively couples solenoid coil 308 to ground, thereby enablingsolenoid coil 308 to conduct a coil current 806, illustrated in FIG. 8.Coil current 806 is illustrated with respect to a vertical axis forAmperage ranging from zero milliamp (mA) to 700 mA. Coil current 806 isillustrated as generally non-zero; however, coil current 806, forcertain embodiments of solenoid valve 300, may be zero or nearly zeroamperes in durations where solenoid valve 300 is closing, i.e., theclosing threshold current is at or nearly zero amperes. Switch 708 iscontrolled by an NFET control signal 808, illustrated in FIG. 8. NFETcontrol signal 808 is illustrated as a discrete signal, i.e., having anon state and an off state.

Drive circuit 700 includes a flyback circuit that includes a capacitor710, a feed diode 712, and an over-voltage protection diode 714. Assolenoid coil 308 is de-energized, an inverse potential develops acrosssolenoid coil 308 and solenoid coil 308 discharges stored energy overtime. Solenoid 308 discharges stored energy through feed diode 712 andcharges capacitor 710. The potential generated across capacitor 710represents potential 804 to which high voltage bus 704 is charged.

In certain embodiments, drive circuit 700 includes a charge pump circuit716. Charge pump circuit 716 is configured to periodically andmomentarily change the reference of capacitor 710 to boost potential 804of high voltage bus 704 with respect to ground prior to opening orclosing valve 300. Charge pump circuit 716 includes FET devices 718 and720 configured to selectively reference capacitor 710 to ground, to lowvoltage bus 702, or, in certain embodiments, capacitor 710 is allowed to“float,” i.e., as an open circuit. In alternative embodiments, one orboth of FET devices 718 and 720 may be a BJT, an IGBT, or anelectromechanical relay. When referenced to low voltage bus 702, i.e.,capacitor 710 is coupled in series with low voltage bus 702, thepotential 804 of high voltage bus 704 with respect to ground becomes asum of the low voltage bus 702 potential and the potential acrosscapacitor 710. FET devices 718 and 720 are controlled to producealternating periods of charging and discharging. The periods of chargingand discharging are illustrated in FIG. 8 by a charge pump bias signal812, which alternates between bias to ground and low voltage bus 702,e.g., 12 VDC. Generally, charge pump bias signal 812 indicates capacitor710 is referenced, or biased, to ground for a majority of a cycleduration. Capacitor 710 is referenced to low voltage bus 702 for a briefduration that corresponds to discharging capacitor 710 when opening thevalve. Further, FET devices 718 and 720 are controlled by independentsignals such that FET devices 718 and 720 are not both closed at anypoint in time (thereby preventing a short to ground). Further, both FETdevices 718 and 720 are controlled to open when capacitor 710 is allowedto float, i.e., an open circuit.

In certain embodiments, where capacitor 710 is allowed to float,solenoid coil 308 is forced to discharge through over-voltage protectiondiode 714, which has a high reverse-bias voltage of, for example, 90-100Volts. In such an embodiment, potential 804 on high voltage bus 704 isincreased to the reverse-bias voltage for a brief duration, rather thana potential across capacitor 710.

During operation, drive circuit 700 operates valve 300 according to avalve control signal 802, illustrated in FIG. 8. Valve control signal802 defines a PWM pattern of opening and closing valve 300. Morespecifically, valve 300 opens on a rising edge 816 and closes on afalling edge 818. Otherwise, valve 300 is maintained in either theclosed 820 or opened position 822.

When valve 300 is in closed position 820, high voltage bus 704 isdisconnected from solenoid coil 308, as illustrated by PFET controlsignal 810 leading up to rising edge 816 of valve control signal 802.Solenoid coil 308 is energized via low voltage bus 702 and a PWM signalrepresented by NFET control signal 808. The frequency and duty cycle ofNFET control signal 808 are regulated to hold coil current 806 below anopening threshold 824 and to charge high voltage bus 704, as illustratedby the increase 826 in potential 804 leading up to rising edge 816. Thefrequency and duty cycle of NFET control signal 808 correspond toperiods of charge and discharge of solenoid coil 308, as illustrated incoil current 806 and, more specifically, peak-to-peak variations in coilcurrent 806 leading up to rising edge 816. Notably, the frequency ofNFET control signal 808 increases leading up to rising edge 816. Incertain embodiments, the frequency of NFET control signal 808 maydecrease slowly and then increase sharply just before rising edge 816.

Charge pump circuit 716 is activated momentarily prior to rising edge816, as illustrated by charge pump bias signal 812. More specifically,reference of capacitor 710 is switched from ground to low voltage bus702 for a brief duration prior to rising edge 816 and corresponding to amomentary increase 828 in potential 804 on high voltage bus 704.

At rising edge 816, valve 300 is actuated, i.e., poppet 312 istranslated from the closed position 820 to the opened position 822. Theactuation corresponds to application of potential 804 on high voltagebus 704 to solenoid coil 308, as illustrated in PFET control signal 810.The increased potential 828 is applied with 100% duty cycle for a briefduration, illustrated by NFET control signal 808, to solenoid coil 308,enabling coil current 806 to exceed opening threshold 824 as quickly aspossible.

When valve 300 is in the opened position 822, potential 804 on highvoltage bus 704 is reduced and PFET control signal 810 controls switch706 to disconnect high voltage bus 704 from solenoid coil 308. Chargepump circuit 716 re-references capacitor 710 to ground to enablecharging. Solenoid coil 308 continues to be energized via low voltagebus 702 and NFET control signal 808 resumes PWM operation with a reducedfrequency and a duty cycle configured to regenerate potential 804 onhigh voltage bus 704. Further, the frequency and duty cycle of NFETcontrol signal 808 are regulated to maintain coil current 806 aboveclosing threshold 830.

Leading up to falling edge 818, at which point valve 300 is closed,i.e., poppet 312 translates from opened position 822 to closed position820, the frequency of NFET control signal 808 is increased to maintaincoil current 806 just above closing threshold 830 such that, whenfalling edge 818 arrives and switch 708 is opened, coil current 806falls below closing threshold 830 as quickly as possible. Again, chargepump circuit 716 switches the reference on capacitor 710 to low voltagebus 702 and corresponding to a momentary increase in potential 804 onhigh voltage bus 704. The momentary higher potential 832 on high voltagebus 704 further reduces the time necessary for solenoid coil 308 todischarge when de-energized.

Once valve 300 is back in closed position 820, NFET control signal 808resumes PWM operation, capacitor 710 is re-referenced to ground, andsolenoid coil 308 resumes cycles of charging and discharging to rechargehigh voltage bus 704.

FIG. 9 is a schematic diagram of an exemplary drive circuit 900 for usewith solenoid valve 300 and solenoid coil 308 shown in FIG. 3. Method500 shown in FIG. 5 may also be embodied in drive circuit 900.

Drive circuit 900 includes a 12V bus 902 (a first node) and a negativelycharged node, or “sub-ground” 904 (a second node). A potential onsub-ground 904 may range from zero Volts DC to −24 Volts DC, or evenfrom zero Volts DC to −50 Volts DC.

Power supplied to solenoid coil 308 is regulated by a switch 906 and aswitch 908. In certain embodiments, power supplied to solenoid coil 308is further regulated by a current throttling circuit 932. Switch 906 isillustrated as a NFET device that selectively couples sub-ground 904 tosolenoid coil 308. Switch 906 is controlled by a NFET control signal910. NFET control signal 910 is illustrated as a discrete signal, i.e.,having an on state and an off state.

Switch 908 is illustrated as a PFET device that selectively couplessolenoid coil 308 to 12V bus 902, thereby enabling solenoid coil 308 toconduct a coil current, similar to coil current 806 illustrated in FIG.8 and ranging from zero mA to 700 mA. Switch 908 is controlled by a PFETcontrol signal 912. PFET control signal 912 is illustrated as a discretesignal, i.e., having an on state and an off state.

Drive circuit 900 includes a flyback circuit that includes capacitors914 and 916, a feed diode 918, and an over-voltage protection diode 920.When solenoid coil 308 is de-energized, an inverse potential developsacross solenoid coil 308 and solenoid coil 308 discharges stored energyover time. Solenoid 308 discharges stored energy through feed diode 918and charges capacitor 914 and 916. The potential generated acrosscapacitors 914 and 916 represents the potential to which sub-ground 904is negatively charged.

In certain embodiments, drive circuit 900 includes a charge pump circuit922. Charge pump circuit 922 is configured to periodically andmomentarily change the reference of capacitor 914 to boost a negativepotential of sub-ground 904 with respect to ground prior to opening orclosing valve 300. Charge pump circuit 922 includes FET devices 924 and926 configured to selectively reference capacitor 914 to ground, to 12Vbus 902, sub-ground 904, or, in certain embodiments, capacitor 914 isallowed to “float,” i.e., as an open circuit. Additionally, FET devices924 and 926 are controlled such that they are not both closed at thesame time (to prevent a short from 12V bus 902 to ground).

Charge pump circuit 922 is controlled by a charge control signal 928 anda discharge control signal 930. More specifically, charge control signal928 commutates FET 924 to couple, or reference, capacitors 914 and 916between 12V bus 902 and ground. When referenced to 12V bus 902,capacitor 914 is charged (at its negative pole) through a diode 927 anda resistor 929. Feed diode 918 further charges capacitor 914 negativelyduring operation as described above.

Discharge control signal 930 commutates FET 926 to couple, or reference,capacitors 914 and 916 between ground and sub-ground 904. Morespecifically, FET 926 is closed to couple the positive pole of capacitor914 to ground, thereby making the potential across capacitors 914 and916 the potential of sub-ground 904. When referenced to ground and whenswitch 906 is closed, the potential at sub-ground 904, or acrosscapacitors 914 and 916, and the potential on 12V bus 902 momentarily addto increase the potential applied across solenoid coil 308.

Charge control signal 928 and discharge control signal 930 areillustrated as discrete signals alternating logical high and lowvoltages. In certain embodiments, where capacitors 914 and 916 areallowed to float, solenoid coil 308 is forced to discharge throughover-voltage protection diode 920, which has a high reverse-bias voltageof, for example, 90-100 Volts. In such an embodiment, the potentialacross 12V bus 902 and sub-ground 904 is increased to the reverse-biasvoltage for a brief duration, rather than a potential across capacitors914 and 916.

During operation, drive circuit 900 operates valve 300 according tovalve control signal 912. Valve control signal 912 defines a PWM patternof opening and closing valve 300. More specifically, valve 300 opens ona rising edge and closes on a falling edge. Otherwise, valve 300 ismaintained in either the closed or opened position.

Drive circuit 900 includes a current throttling circuit 932 that enablesa calibrated amount of current to be conducted by solenoid coil 308 andmaintain the coil current just below an opening threshold when valve 300is in the closed position. Conversely, current throttling circuit 932enables a calibrated amount of current to be conducted by solenoid coil308 when valve 300 is in the opened position, where the coil current ismaintained just above a closing threshold for valve 300.

Current throttling circuit 932 includes a bipolar junction transistor(BJT) 934 coupled between solenoid coil 308 and ground, and in serieswith 12V bus 902 and solenoid coil 308. The current conducted throughsolenoid coil 308 is controlled by the gain of BJT 934. BJT 934 iscontrolled by a throttling control signal 936. In certain embodiments,throttling control signal 936 is an analog control signal generated by,for example, an analog output from a microprocessor or adigital-to-analog converter (DAC) integrated therein or providedseparately. Further, in certain embodiments, the analog signal isbuffered, for example, by an op-amp before being provided to BJT 934,thereby enabling an appropriate amount of current to be delivered to BJT934 to achieve the desired current through solenoid coil 308. Further,in certain embodiments, the analog signal may be pulsed off and on in aPWM fashion. Current throttling circuit 932 includes a Schottkyrectifier diode 938 that prevents current from conducting fromsub-ground 904 through BJT 934 to ground when opening solenoid valve300. It should be understood that current throttling circuit 932 may beused independently of certain aspects of drive circuit 900 and, in someembodiments, may be used as a drive circuit by itself.

In certain embodiments, current throttling circuit 932 is configured tomodulate current conducted through solenoid coil 308 based on areal-time current measurement. Drive circuit 900 includes a currentmeasurement circuit 940 that, in certain embodiments, provides a currentmeasurement signal 942 to a microprocessor for controlling throttlingcontrol signal 936 and, consequently, to adjust the current conductedthrough solenoid coil 308. Current measurement circuit 940 includes acurrent sense resistor 944 coupled in series with solenoid coil 308. Incertain embodiments, as illustrated in FIG. 9, current sense resistor944 is further coupled in series with charge pump circuit 922. Inalternative embodiments, a separate current measurement circuit may beprovided for measuring current supplied to charge pump circuit 922. Infurther alternative embodiments, current measurement for charge pumpcircuit 922 may be omitted entirely. Current measurement circuit 940includes a current sense amplifier 946 coupled across current senseresistor 944 and configured to detect the voltage drop across currentsense resistor 944 and output the current measurement signal 942.Current measurement signal 942, depending on when the measurement iscollected, represents the current conducted through solenoid coil 308 orthe current supplied to charge pump circuit 922.

Drive circuit 900 includes a flyback diode 948 coupled in parallel withsolenoid coil 308. Flyback diode 948 slows the dissipation of coilcurrent from solenoid coil 308 when switch 906 or BJT 934 are switchedat a high frequency. By slowing the dissipation, or decay, flyback diode948 enables the coil current to remain substantially constant, and abovea threshold at which valve 300 would close, when switching switch 906 orBJT 934 at a high frequency and suitable duty cycle, e.g., when thevalve is being held in the opened position by a high frequency PWM NFETcontrol signal 910 or a high frequency PWM signal applied to BJT 936.Flyback diode 948 is a low forward voltage diode, such as a Schottkydiode or a germanium diode. Low-forward voltage diodes generally have aforward voltage in a range of about 150 millivolt to 450 millivolt. Inalternative embodiments, flyback diode 948 is a typical silicon diode orother diode having a forward voltage of about 0.7 millivolt or higher,although such an embodiment may not perform as well. Generally, the rateat which solenoid coil 308 discharges its stored energy is directlyrelated to a voltage drop across solenoid coil 308, which is further afunction of the back EMF generated to force current to conduct throughflyback diode 948, feed diode 918, or protection 920. Accordingly, thelower the forward voltage of flyback diode 948, the lower the voltagedrop across solenoid coil 308, and the slower energy is dissipated fromsolenoid coil 308. In other words, a lower forward voltage enables aslower dissipation of the coil energy and, consequently, a more-steadycoil current as switch 906 or BJT 934 are switched at a high frequency.

Charge pump circuit 922 is activated, via discharge control signal 930,a duration of time prior to closing switch 908. More specifically,capacitors 914 and 916 are coupled between 12V bus 902 and sub-ground904 for a brief duration prior to a rising edge of PFET control signal912 and corresponding to a momentary increase in negative potential onsub-ground 904.

At the rising edge of PFET control signal 912, valve 300 is actuated,i.e., poppet 312 is translated from the closed position to the openedposition. The actuation corresponds to application of the potentialacross 12V bus 902 and sub-ground 904 to solenoid coil 308. Theincreased potential is applied with 100% duty cycle for a brief durationby NFET control signal 910, to solenoid coil 308, enabling the coilcurrent to exceed the opening threshold of valve 300 as quickly aspossible.

Once valve 300 is transitioned to the opened position, FET 926 is openedto stop discharge of capacitors 914 and 916. In certain embodiments,capacitors 914 and 916 are re-connected to 12V bus 902 a short timelater to begin recharging. In alternative embodiments, charge controlsignal 928 closes FET 924 after valve 300 is de-energized by openingswitch 908. In further alternative embodiments, charge control signal928 is a PWM signal having a frequency and duty cycle to chargecapacitors 914 and 916 during “off” periods of switch 908.

Once valve 300 is transitioned to the opened position, switch 906 isopened to remove application of the potential on sub-ground 904. Currentthrottling circuit 932 remains active, i.e., BJT 934 is closed, toenable enough coil current to conduct through solenoid coil 308 tomaintain poppet 312 in the opened position. The coil current ismaintained just above the threshold at which valve 300 closes (i.e., theclosing threshold), such that, when the rising edge of PFET controlsignal 912 arrives, coil current falls below the threshold as quickly aspossible and valve 300 closes.

In an alternative embodiment, similar to drive circuit 700 (shown inFIG. 7), where current throttling circuit 932 is omitted, BJT 934 isreplaced by an NFET device that is controlled by an NFET control signalat a variable frequency and duty cycle to maintain the coil current justbelow an opening threshold when valve 300 is in the closed position.Conversely, the NFET device is controlled (e.g., with a PWM signal or anamplifier FET) to enable a calibrated amount of current to be conductedby solenoid coil 308 when valve 300 is in the opened position, where thecoil current is maintained just above a closing threshold for valve 300.In such an embodiment, when valve 300 is in a closed position,capacitors 914 and 916 are decoupled from ground by opening FET 926.Solenoid coil 308 is energized by 12V bus 902 according to PFET controlsignal 912, which is generated as a PWM signal by a microprocessor orother suitable processing device to have a desired frequency and dutycycle. The frequency and duty cycle of PFET control signal 912 areregulated to hold the coil current below an opening threshold for valve300. In embodiments having charge pump circuit 922, FET 924 iscommutated to close and enable charging of capacitors 914 and 916 usingcurrent that is “free-wheeled” by feed diode 918 as switch 908 isswitched at a high frequency. The frequency and duty cycle of PFETcontrol signal 912 correspond to periods of charge and discharge ofsolenoid coil 308. The frequency of PFET control signal 912 increasesleading up to the opening or closing of solenoid valve 300. In certainembodiments, the frequency of PFET control signal 912 may decreaseslowly and then increase sharply just before the opening of solenoidvalve 300.

When valve 300 is to be opened, NFET control signal 910 is generated asa 100% duty cycle signal to enable coil current to increase above theopening threshold as quickly as possible. Additionally, as describedabove, discharge control signal 930 couples capacitors 914 and 916 toground, and charge control signal 928 opens FET 924, thereby enablingdischarge of charge pump circuit 922. Discharge of capacitors 914 and916 develops a negative potential on sub-ground 904, which adds to thepotential of 12V bus 902 and is applied across solenoid coil 308.

Once valve 300 is opened, i.e., poppet 312 translates to the openedposition, discharge of charge pump circuit 922 is disabled, solenoidcoil 308 continues to be energized via 12V bus 902, BJT 934 remainsclosed, and PFET control signal 912 resumes PWM operation with a reducedfrequency and a duty cycle configured to regenerate the potential acrosscapacitors 914 and 916. Further, the frequency and duty cycle of PFETcontrol signal 912 are regulated to maintain the coil current above aclosing threshold.

Prior the valve 300 closing, the frequency of PFET control signal 912 isincreased to maintain the coil current just above the closing thresholdsuch that, when the duty cycle of PFET control signal 912 is reduced tozero, the coil current falls below the closing threshold as quickly aspossible.

Once valve 300 is back in a closed position, PFET control signal 912resumes PWM operation, capacitors 914 and 916 are re-referenced between12V bus 902 and sub-ground 904, and solenoid coil 308 resumes cycles ofcharging and discharging to recharge capacitors 914 and 916.

FIG. 10 is a perspective view of one embodiment of a fluid applicationsystem 100. Fluid application system 100 includes a volatile liquidfertilizer application system for application of fertilizers such as,for example, anhydrous ammonia. Fluid application system 100 includes amotorized vehicle 102, a fluid storage tank 104, and a distributionmanifold 106. Motorized vehicle 102 may be any machine that enablesfluid application system 100 to function as described herein. Insuitable embodiments, one or more components of fluid application system100 may be incorporated into motorized vehicle 102 without departingfrom some aspects of this disclosure. In the exemplary embodiment, fluidstorage tank 104 and distribution manifold 106 are disposed on a wheeledchassis 108 towed behind motorized vehicle 102.

During operation, fluid storage tank 104 may contain any type of fluidfor distribution by fluid application system 100. For example, fluidstorage tank 104 may store a volatile fluid intended to be applied tofields for agricultural purposes. A common fluid used for agriculturalpurposes is anhydrous ammonia, which is applied to fields primarily as afertilizer to increase the nutrient level of soils. The anhydrousammonia includes at least some gaseous substance and, therefore, ismaintained at a carefully controlled pressure to control the gaseousproperties. In the exemplary embodiment, fluid storage tank 104 isconfigured to store and maintain the fluid at a desired pressure asfluid flows out of the fluid storage tank. Fluid application system 100includes at least one pump 130 connected to fluid storage tank 104 tofacilitate maintaining the fluid in the fluid storage tank at thedesired pressure.

In the exemplary embodiment, fluid storage tank 104 is fluidly connectedto a distribution manifold 106 by a fluid line 132. Disposed betweendistribution manifold 106 and fluid storage tank 104 is a valve 136 andquick connect 134. In suitable embodiments, quick connect 134 and valve136 may be coupled to any portions of fluid application system 100. Forexample, in some suitable embodiments, any of quick connect 134 andvalve 136 may be omitted without departing from some aspects of thisdisclosure. In the exemplary embodiment, quick connect 134 facilitatesfluid storage tank 104 being connected to and removed from fluid line132. Valve 136 controls fluid flow through fluid line 132. For example,valve 136 is positionable between a closed position where fluid isinhibited from flowing through fluid line 132 and an open position wherefluid is allowed to flow through fluid line 132. In certain embodiments,valve 136 may be any valve that enables fluid application system 100 tofunction as described herein.

The fluid is directed from fluid line 132 through valve 136 and intodistribution manifold 106. As shown in FIGS. 9 and 10, distributionmanifold 106 includes a plurality of supply lines 138 each connected tovalve assemblies 36. Each valve assembly 36 regulates flow of the fluidinto a dispensing tube 140 for injecting the fluid into a soil.Distribution manifold 106 distributes the fluid to valve assemblies 36and dispensing tubes 140 for emitting the fluid from fluid applicationsystem 100.

Each valve assembly 36 is controlled by a controller. The controller maybe configured to control flow through dispensing tubes 140 using themethods described above with reference to FIGS. 3A-8.

In suitable embodiments, fluid application system 100 may include anynumber of dispensing tubes 140. In some embodiments, as the fluid isemitted from dispensing tubes 140, vehicle 102 moves fluid applicationsystem 100 along a desired path for fluid application, such as rows 146of a field 148. In the exemplary embodiment, dispensing tubes 140 areconnected to or positioned behind a soil preparation mechanism 142, suchas a knife or plow that contacts the soil as dispensing tubes 140dispense fluid onto the soil, as best seen in FIG. 11. Soil preparationmechanisms 142 are connected to a boom 143, which is connected to andpulled behind vehicle 102.

The technical effects of the systems, apparatus, and methods describedherein include: (a) reducing turn-on time and turn-off time for solenoidvalves; (b) providing a second node configured to be charged to a secondvoltage that is either a high voltage or a negative voltage usingsolenoid coils that are environmentally sealed, isolated from controlelectronics, have relatively large inductance, and have sufficient powercapacity for boost converting without any additional cost, size, orweight; (c) reducing overall power consumption by regulating currentsnear opening and closing thresholds; (d) reducing power dissipationwithin the drive circuit by the use of electromagnetic field energystored in the solenoid coil and by utilizing the flyback currents tocharge a second node.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other and examples areintended to be within the scope of the claims if they include structuralelements that do not differ from the literal language of the claims, orif they include equivalent structural elements with insubstantialdifferences from the literal language of the claims.

What is claimed:
 1. A drive circuit for controlling a solenoid valvehaving a solenoid coil and a poppet configured to translate therein,said circuit comprising: a first node configured to be energized by apower source at a first voltage; a second node configured to beenergized to a second voltage; a control circuit coupled to said firstnode and said second node, and configured to: couple said first node andsaid second node in series with the solenoid coil to apply a combinationof the first voltage and the second voltage to the solenoid coil; andperiodically energize the solenoid coil using a pulse- width-modulated(PWM) signal having a frequency and a duty cycle configured to regulatea current conducted through the solenoid coil to translate the poppetbetween an opened position and a closed position within the solenoidvalve, and to maintain the poppet in the opened position; and a flybackcircuit coupled to the solenoid coil and configured to energize saidsecond node with energy stored in the solenoid coil.
 2. The drivecircuit of claim 1, wherein said control circuit is further configuredto: adjust the duty cycle of the PWM signal to 100 percent to translatethe poppet toward an open position.
 3. The drive circuit of claim 1,wherein said control circuit is further configured to: decouple thesolenoid coil from said second node; couple the solenoid coil to saidfirst node to apply the first voltage to the solenoid coil; and adjustthe frequency and the duty cycle of the PWM signal to maintain thepoppet in an opened position.
 4. The drive circuit of claim 1, whereinsaid control circuit is further configured to: decouple the solenoidcoil from said second node; couple the solenoid coil to said first nodeto apply the first voltage to the solenoid coil; and adjust thefrequency and the duty cycle of the PWM signal to regulate the currentconducted through the solenoid coil below an opening threshold fortranslating the poppet to an open position, thereby maintaining thepoppet in a closed position.
 5. The drive circuit of claim 4, whereinsaid control circuit is further configured to adjust the frequency andthe duty cycle of the PWM signal to limit the current conducted throughthe solenoid coil to below the opening threshold, wherein the openingthreshold is determined based on a measured fluid pressure differentialacross the solenoid valve.
 6. The drive circuit of claim 5, wherein saidcontrol circuit is further configured to: couple the solenoid coil tosaid second node to apply the first voltage and the second voltage tothe solenoid coil; and increase the duty cycle of the PWM signal to 100percent to translate the poppet toward an open position.
 7. The drivecircuit of claim 6, wherein said control circuit is further configuredto adjust the duty cycle of the PWM signal to increase the currentconducted through the solenoid coil to above a closing thresholddetermined based on the measured fluid pressure differential across thesolenoid valve.
 8. The drive circuit of claim 6, wherein said controlcircuit is further configured to increase the frequency of the PWMsignal to at least 1000 Hertz prior to coupling the solenoid coil tosaid second node.
 9. The drive circuit of claim 4, wherein said controlcircuit is further configured to regulate the frequency of the PWMsignal to no more than 40 Hertz.
 10. The drive circuit of claim 1,wherein said control circuit is further configured to periodicallycouple said first node and said second node to the solenoid coilaccording to a valve-pulsing PWM signal.
 11. The drive circuit of claim1 further comprising a current sensor configured to measure the currentconducted through the solenoid coil, wherein said control circuit isfurther configured to adjust the frequency and duty cycle of the PWMsignal based on the measured current.
 12. The drive circuit of claim 1,wherein said control circuit is further configured to adjust the dutycycle of the PWM signal to below 50 percent.